Valves are used in numerous types of industries for a wide variety of purposes. The word "valve" is commonly used to describe any device that permits fluid flow or regulates fluid flow of whatever fluid is contained in a pipe or tube. Usually, fluid flow control is achieved by the use of a flap, lid or plug that may be closed or clamped to prohibit flow, or opened to permit flow. Additionally, a common type of valve found is a gate valve that opens and closes by rotating pivotally around a hinge. The gate is opened by placing it in a position parallel to the fluid movement and permits fluid flow. When the gate is turned perpendicular to fluid flow, it restricts or prohibits any flow.
The problem with many types of valves is that they are not very fast-acting, in that they require turning or clamping of the valve which takes time. As a result, when one initially starts to open a valve, a small amount of fluid is let through the valve. The amount of fluid passing through then increases as the valve is continued open. The same is true for closing a valve. As one closes a valve, fluid will continue to flow through the valve until the valve is completely shut. There is always some volume of fluid that passes through the valve after one starts to close a valve, referred to as residual pass-through.
There is a need for a valve which is fast acting and which, when opened or closed, will open or close quickly and widely to permit a large volume of fluid to pass through when open and minimize residual pass-through when closed. One industry concerned with developing such a fast-acting high-output valve is the turbine engine industry.
Gas turbine engines require high performance and high reliability in order to assure that flights can be completed effectively, efficiently and safely. This is especially true in military applications. Air is forced through the inlet or mouth of a turbine engine and from there directed into a turboshaft or turbojet axial compressor. As the flow in such an axial compressor is reduced or made non-uniform while the compressor or rotational speed is held constant, a point will be reached at which some or all of the engine blades begin to stall and engine instabilities occur. The most violent of these is "surge", which for high speed compressors (as in a turbine engine) can result in periodically reversed flow and mechanical damage. The other result of air being reduced or made non-uniform is rotating stall. "Stall" can result in a region of blocked flow covering half of the circumference of the engine inlet and rotating at half the rotor speed, and may lock the engine.
When a gas turbine engine experiences a compressor "stall", the given flight will be effected. In cases of severe stall, the engine or drive train components can lock or freeze, causing loss of engine operation. When this happens in flight, the results can be catastrophic. For an in depth discussion of how a turbine engine works, and turbine engine surge and stall, see Emmons, H. W., Pearson, C. E., and Grant, H. P.; "Compressor Surge and Stall Propagation," Transactions of the ASME, May, 1955, p. 455-469; and Greitzer, E. M.; "The Stability of Pumping Systems--the 1980 Freeman Scholar Lecture,-- ASME J. of Fluids Engineering, June, 1981, vol. 103, p. 193-242.
Surge and stall have three causes: (1) engine deterioration; (2) aerodynamic distortions (especially at the air inlet); and (3) hot gas injection (from weapon firing). Despite the knowledge of these causes, there has been little success in providing turbine engines with any reliable way of preventing engine surge or stall. Research has indicated, however, that the inception of a flow disruption in compressor rotors (referred to above as rotating "stall") can be delayed by locally affecting the air flow conditions of the critical compressor stage rotor.
The air flow conditions can be locally modified by bleeding air from behind the affected rotor, or injecting air in front of the affected rotor. This results in improved performance for the compression system. Successful control of rotating stall allows improved performance of turbomachinery which reduces operating, replacement and repair costs. An injection valve to inject air in front of an affected rotor or a bleed valve to extract air behind a rotor, however, must be able to cycle from full close to full open to full close at a very fast speed (approximately 150 Hz), and must be sized to pass a maximum of approximately 1.65 cubic feet of air per second at standard day conditions.
Accordingly, it is an object of the present invention to provide a fast-acting high-output valve capable of opening and closing at a high rate of speed, and which permits a large volume of fluid to pass through said valve.
It is a further object of the invention to provide a fast-acting high-output valve capable of injecting air in front of a compressor or bleeding off air behind a compressor in a turbine engine to reduce rotating stall.
All references referred to above are incorporated herein by reference.